1. Field of the Invention
The present invention relates to a yoke and a manufacturing method thereof, and more particularly, to a yoke which can define a magnetic path in an actuator, and a manufacturing method thereof.
2. Description of the Related Art
A yoke, which is made of a metallic material, is generally manufactured by pressing a metal plate. In more detail, the yoke is consecutively manufactured in a progressive mold. That is, the yoke is formed in a designed shape by passing a base material elongated in a band shape through the progressive mold and sequentially processing the base material. In a process of forming inner yoke portions, the inner yoke portions have a desired height by partially bending and drawing the base material.
The yoke includes a plate-shaped base. The inner yoke portions are formed upright to face each other at both ends of a center vent of a center portion of the base. Two support protrusions are formed at the leading end of each of the inner yoke portions. The leading ends of the support protrusions support a bottom surface of a cover for protecting a coil and an optical member of an actuator.
Meanwhile, a portion between the pair of support protrusions is perforated such that the perforated portion is a path of light emitted to test tracking performance in the production of the actuator. When used in the actuator, the inner yoke portions are installed to pass through a bobbin.
However, the aforementioned related art has the following problems.
In order to form each of the inner yoke portions, only about a half of one side width of the center vent can be used as a length of the inner yoke portion. Therefore, the inner yoke portion should be extended to have a designed length through a drawing process. However, if the drawing process is carried out once in order to obtain the designed value of the inner yoke portion, the inner yoke portions may be ruptured or not be formed in a precise size. Thus, the drawing process should be performed at least twice. Accordingly, it is difficult to form the inner yoke portion and the base portion adjacent thereto to have the size and shape according to the design.
Particularly, since the designed value of the inner yoke portion is at least twice as large as the length in the base material state before the drawing process, it is difficult to control the size of the inner yoke portion due to a crack or rupture. For reference, comparing a thickness t1 of the base material before the drawing process with a thickness t2 thereof after the drawing process, t1 is about a half of t2, i.e., t1=0.5t2. In addition, as the size of the center vent is limited, the increase of the length of the inner yoke portion is restricted.
In the related art, the pair of support protrusions are formed at the leading end of each of the inner yoke portions. Therefore, it is very cumbersome to perform a process of attaching a reflecting plate for measuring a tracking property of the bobbin in the actuator to an objective lens of the bobbin through the inner yoke portions.